The storage runtime interface should not enforce a hash type (#4231)

* The storage runtime interface should not enforce a hash type

Currently the runtime interface enforces `H256` as hash type, but in the
future people could use whatever they want as hash type. The hash type
always needs to match between the runtime and the node, but that is
already required.

* Update primitives/externalities/src/lib.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

substrate/primitives/trie/src/lib.rs

@@ -167,39 +167,45 @@ pub fn read_trie_value_with<
 }
 
 /// Determine the default child trie root.
-pub fn default_child_trie_root<L: TrieConfiguration>(_storage_key: &[u8]) -> Vec<u8> {
-	L::trie_root::<_, Vec<u8>, Vec<u8>>(core::iter::empty()).as_ref().iter().cloned().collect()
+pub fn default_child_trie_root<L: TrieConfiguration>(
+	_storage_key: &[u8],
+) -> <L::Hash as Hasher>::Out {
+	L::trie_root::<_, Vec<u8>, Vec<u8>>(core::iter::empty())
 }
 
 /// Determine a child trie root given its ordered contents, closed form. H is the default hasher,
 /// but a generic implementation may ignore this type parameter and use other hashers.
-pub fn child_trie_root<L: TrieConfiguration, I, A, B>(_storage_key: &[u8], input: I) -> Vec<u8>
+pub fn child_trie_root<L: TrieConfiguration, I, A, B>(
+	_storage_key: &[u8],
+	input: I,
+) -> <L::Hash as Hasher>::Out
 	where
 		I: IntoIterator<Item = (A, B)>,
 		A: AsRef<[u8]> + Ord,
 		B: AsRef<[u8]>,
 {
-	L::trie_root(input).as_ref().iter().cloned().collect()
+	L::trie_root(input)
 }
 
 /// Determine a child trie root given a hash DB and delta values. H is the default hasher,
 /// but a generic implementation may ignore this type parameter and use other hashers.
-pub fn child_delta_trie_root<L: TrieConfiguration, I, A, B, DB>(
+pub fn child_delta_trie_root<L: TrieConfiguration, I, A, B, DB, RD>(
 	_storage_key: &[u8],
 	db: &mut DB,
-	root_vec: Vec<u8>,
-	delta: I
-) -> Result<Vec<u8>, Box<TrieError<L>>>
+	root_data: RD,
+	delta: I,
+) -> Result<<L::Hash as Hasher>::Out, Box<TrieError<L>>>
 	where
 		I: IntoIterator<Item = (A, Option<B>)>,
 		A: AsRef<[u8]> + Ord,
 		B: AsRef<[u8]>,
+		RD: AsRef<[u8]>,
 		DB: hash_db::HashDB<L::Hash, trie_db::DBValue>
 			+ hash_db::PlainDB<TrieHash<L>, trie_db::DBValue>,
 {
 	let mut root = TrieHash::<L>::default();
 	// root is fetched from DB, not writable by runtime, so it's always valid.
-	root.as_mut().copy_from_slice(&root_vec);
+	root.as_mut().copy_from_slice(root_data.as_ref());
 
 	{
 		let mut trie = TrieDBMut::<L>::from_existing(&mut *db, &mut root)?;
@@ -212,7 +218,7 @@ pub fn child_delta_trie_root<L: TrieConfiguration, I, A, B, DB>(
 		}
 	}
 
-	Ok(root.as_ref().to_vec())
+	Ok(root)
 }
 
 /// Call `f` for all keys in a child trie.